1. Field of the Invention:
This invention relates in general to subsea wells, and in particular to a means for stabilizing within an outer housing an inner housing that secures to a riser leading to the surface.
2. Description of the Prior Art:
In a subsea well of the type concerned herein, a guide base will be placed on the sea floor. An outer housing will be inserted into the guide base. The outer housing has large diameter conduit, typically 30 inch, that extends into the earth a selected distance. The 30 inch conduit will be cemented in place.
Then, an inner housing will be lowered into the outer housing. The inner housing will be secured to lesser diameter casing, normally about 20 inch. The 20 inch casing will be cemented in place. Typically, there will be a clearance between the outer housing interior and the inner housing exterior. A riser will extend from the inner housing to the drilling vessel.
The drilling vessel will be floating, and thus is subject to wave and wind action. The riser will bend as the drilling vessel moves relative to the subsea well. This causes a bending action on the inner housing. There is a possibility that the repetitive movement could cause fatigue of the inner housing. This could cause the inner housing to part.
Cement located between the inner and outer housing helps to prevent relative movement. Also, long tapered sections extend downward from the inner housing to the casing to reduce the bending stress. While this is successful, these long tapered sections are expensive to manufacture. Also, if the cement does not extend high enough in the clearance between the inner and outer housings, support for bending movement would be lacking.
There have been proposals in the past to stabilize the inner housing within the outer housing by means of slips and slip rings, such as shown in U. S. Pat. No. 4,499,950, Bruce J. Watkins, issued Feb. 19, 1985, and U.S. Pat. No. 4,751,968, Thomas J. Ames, et al, issued June 21, 1988. Improvements are desirable.
Also, if the well is to be abandoned subsequently it is desirable to remove and retrieve the inner housing. The operator can cut the casing below the inner housing. However, pulling the inner housing from the outer housing can be difficult.